The present invention relates in general to a temperature sensing device, and more particularly, to a device for monitoring on a real time basis the temperature of heated vessels at preselected locations along the length of the vessel.
Commercial processes, such as those typically found in the chemical industry, require the continuous real time monitoring of the process temperature as occurring within large scale reactors or vessels at a various locations. Numerous types of temperature monitoring devices are presently known, a typical device being the thermocouple constructed of dissimilar conductive materials joined together at a junction. Thermocouples have found particular utility in monitoring fluid temperature in commercial processes which are carried out in large scale reactors having a height often reaching 100 feet or more. To accurately monitor the temperature at various locations within the reactor, an enclosed conduit is suspended within the process fluid. A plurality of bundled thermocouples are positioned within the conduit, each having a different length to monitor the temperature at a precise predetermined location along the conduit's length.
In order to obtain an accurate temperature reading, it is required that the thermocouple junction be forceably engaged against the inner wall of the conduit at its respective temperature measuring location. It is understood that one has to insert the thermocouple bundle into the conduit and to do so at lengths of 100 feet or more. Hence, the bundle should be as compact as possible to allow easy insertion. Therefore, the prior art supplied bi-metallic devices to allow the individual thermocouple rods to move outwardly under the influence of temperature to thereby contact the wall of the conduit. The devices therefore enabled one to insert a closely packed thermocouple bundle into a conduit in a rapid and reliable manner, while assuring that each rod contacted the conduit wall when the bundle was exposed to a suitable temperature. Known thermocouple devices, such as disclosed in U.S. Pat. Nos. 3,263,502 and 3,015,234, use such bi-metallic clips which are responsive to the presence of selected temperature ranges for exerting the necessary contact force. However, these bi-metallic clips are prone to deterioration of their spring force when subjected to prolonged high temperatures. This deterioration ultimately prevents sufficient forceable engagement of the thermocouple junction with the conduit to give accurate temperature readings, therefore causing a marked decrease in sensitivity.
Additionally, the frequent cold working of these bi-metallic clips often results in their mechanical failure and then necessitate time consuming repair or replacement. In the event of such failure, the thermocouple loses its contact with the conduit entirely, thereby measuring and recording only the temperature of the dead air within the conduit, which is an inaccurate and unreliable indication of the temperature of the process fluid within the reactor. Accordingly, there is the need for a temperature sensing device of the dynamic type which overcomes and avoids the disadvantages resulting from the use of these bi-metallic clips of the known thermocouple temperature sensing devices.